The present invention relates generally to the field of variable air volume (VAV) controllers for heating, ventilation, and air conditioning (HVAC) systems. The present invention more particularly relates to systems and methods of determining the direction of airflow across a pressure sensor in a VAV controller.
Velocity pressure is one description of air flow in a duct. Velocity pressure is the difference between the total (face) pressure and the static pressure. The static pressure and the face pressure can be measured. At least two hoses or tubes, corresponding to in-flow and out-flow, are attached to the ductwork. The hoses may be connected to a pressure sensor to measure the face pressure.
With a unidirectional or single-ended pressure sensor, face pressure can be measured in only one direction. Accordingly, the face pressure and the static pressure must be measured at the appropriate locations to accurately calculate velocity pressure. Face pressure is measured on the high side (in-flow), and static pressure is measured on the low side (out-flow). The hoses or tubes carrying the air must be connected to the correct side of the pressure sensor so that face pressure is measured on the high side. A bidirectional or bipolar pressure sensor can measure both negative pressure and positive pressure (i.e. air flow in both directions). Nevertheless, a technician may still be required to install the hoses on particular sides of the pressure sensor so that the actual direction of airflow is known.
Bidirectional pressure sensors can lead to confusion or mistakes among technicians in the field, resulting in incorrect (backwards) installations of the hoses to the pressure sensor. Manufacturers and consumers can incur costs relating to the incorrect installation. This includes monetary costs associated with equipment designed to alleviate confusion (e.g., differently colored tubes to designate the side they are to be installed on). This can also include the time required for manual verification of the direction in which the hoses were originally installed, time required for reinstallation of the hoses when they were originally installed backwards, down time during power cycling of the VAV controller, or down time associated with re-commissioning of the VAV controller.
Reducing or omitting manual verification of the hose installation and/or airflow direction is challenging and difficult.